Page:The American Cyclopædia (1879) Volume VII.djvu/43

 EXPLOSIVES 35 bustion of gunpowder has been variously esti- mated. Gatzschmann gives the following ta- ble, compiled from different authorities : Authority. Estimate in atmospheres. 4,000 .. Mver ....................... 8,800 to Scon... ........................... 4,000 Prechtl .............................. 4,400 Kann.rsoh^Heere................. *g ^ ^ Robert ............................... 7,500 Bernoulli .............................. 10,000 Kumford .............................. 29,178 to 54,740 The usual estimate at present is for rifle pow- der 4,000, and for blasting powder 2,000 at- mospheres. It is believed that in practice half these figures are realized. The latest re- searches upon the heat set free by the com- bustion of powder, those of Roux and Sarran (Comptes Rendus, July, 1873), give the fol- lowing results : VARIETIES. COMPOSITION. Calories per kilo- gramme. 807-3 752-9 730-8 694-2 570-2 Weight of gases per kilo- gramme. 0-897 0-412 0-414 0-446 0-499 Nitre. Sul- phur. Char- coal. Fine sporting Cannon 78 75 74 72 62 10 12-5 10-5 18 20 12 12-5 15-5 15 18 B musket Export Blasting The time within which this pressure is devel- oped is an important element in the practical effect. The particles of the powder are suc- cessively ignited and combustion becomes gen- eral. The rate of ignition is more rapid, and that of combustion is slower, the larger the grain of the powder. The finest-grained pow- der, when pressed closely together, behaves like a single mass, burning with comparative slowness, and hence showing less explosive power. It is employed in rockets and fire- works. For rifled guns, a coarse grain is now preferred, since its quick ignition gives the force required to press the projectile into the grooves, while its prolonged combustion aug- ments the pressure until the projectile leaves the gun with maximum velocity. Blasting pow- der, which is required to lift and split, rather than to throw, is usually coarse-grained, though modern practice is tending to the employment of "quicker" powders; a change due to the observed effectiveness of the nitro-glycerine compounds. The composition of ordinary blasting powder, as above shown, effects a slow combustion. A blasting powder now used to a considerable extent in this country contains Chili saltpetre (nitrate of soda) in- stead of nitre. It is unsuitable for sporting or military purposes. Another variation from the usual formula is Oliver's powder, made in Pennsylvania, in which peat is substituted for charcoal, with increased safety of manufacture and cheapness of product. The West Virginia mineral grahamite, a hydrocarbon, has also been experimented upon as a substitute for charcoal, with favorable results. Common powder soaked at the moment of using in nitro-glycerine has been used in Swedish quar- ries, with trebled effectiveness. Dynamite is safer and better. Pyronene is a cheap, infe- rior blasting powder, made of 52*5 parts nitrate of soda, 20 parts sulphur, and 27'5 parts spent tan. In Davey's powder a part of the char- coal is replaced by flour, starch, &c., for safety in preparation. Slow-burning powders used in Germany (Neumeyer's, Kiip's, &c.) contain less sulphur and more coal than the ordinary kind. They are recommended for safety and small amount of smoke. An intimate mixture of 3 parts nitre, 2 parts dry carbonate of potassa, and 1 part sulphur will when slow- ly heated (e.g., in an iron spoon) first melt, and soon after explode with deafening noise. The sulphur acts upon the carbonate of potassa, producing " liver of sulphur," a mixture of the sulphide with the sulphate of potassa; this is suddenly oxidized by the decomposition of the nitric acid, and nitrogen gas is liberated. The experiment should be tried with a small quantity only, say as much as will cover the tip of a knife blade. (See GUNPOWDER.) Pyroxyline. In the explosives classed above under gunpowder, the sulphur plays the part of a stimulant of chemical action, by its supe- rior readiness to ignite. It is the nitric acid and the carbon which, forming voluminous gases, generate the explosive force; and these substances can be brought together in such ways as to form explosive compounds which have the advantage of leaving no solid residues or smoke. Pyroxyline is the name given to the class of detonating substances produced by the action of concentrated nitric acid upon the cellulose of cotton, hemp, paper, sawdust, &c. Gun cotton was discovered in 1846 by Schon- bein, and also by Bottger. The conversion of cotton into gun cotton by the action of nitric acid scarcely changes its outward appearance. Chemically, it contains much hyponitric acid. It will ignite at 50 to 150 0., and leaves no residue after explosion. Its effectiveness is variously estimated at from two to six (prob- ably four) times that of gunpowder. Accord- ing to the best modern formula, gun cotton is trinitro-cellulose, C 6 H7(NO 2 ) 3 O 6. The pro- ducts of combination are entirely gaseous. Karolyi gives the following, in 100 parts: CONSTITUENTS. By volume. By weight. 28-55 19-11 11-17 8-83 8-56 1-85 21-98 28-92 30-43 6-47 9-59 8-71 1-60 14-28 Carbonic acid Marsh gas Binoxide of nitrogen Carbon. . Aqueous vapor 100-00 100-00 When burned under pressure, the nitric oxide reacts more completely with the carburetted hydrogen, and the result of this and other